Dolbier, William R., Jr.; Rong, Xiao X.; Stalzer, Walter E. et. al. in WO 98/24743 (1998) proposes a method for synthesizing α,α,α′,α′-tetrafluoro-p-xylene by a replacement reaction of α,α,α′,α′-tetrachloro-p-xylene.
The following introduces methods for synthesizing α,α,α′,α′-tetrachloro-p-xylene published in the prior art.
U.S. Pat. No. 4,328,374 (1982); U.S. Pat. No. 4,465,865 (1984); JP51006931 (1976); JP560123329 (1981); EP 54634 (1982) and WO 98/24743 (1998) disclose a method for reacting p-xylene with chlorine by a photochlorination reaction according to the following reaction formula:
The abovementioned method needs to use a photoillumination device and the reaction is very difficult to be controlled to form a chlorinated product having just four chlorine substituents. Instead a product mixture containing three or less or five or more chlorine substituents will be produced, and pure products are difficult to be separated from the product mixture due to their similar polarities. For example, the photochlorination reaction disclosed in WO 98/24743 (1998) has a reaction time of 110 hours and a yield lower than 35%. Furthermore, the product mixture contains not only a chlorinated product having four chlorine substituens, but also incomplete and over-reacted products having less than three chlorine atoms and over five chlorine atoms. The product mixture is difficult to be purified.
Mikhailov, V. S.; Matyushecheva, G. I.; Yagupol'shii, L. M.; Zh. Org. Khim., 9(9), 1824 (1973) propose a method for preparing α,α,α′,α′-tetrachloro-p-xylene by reacting p-xylene with phosphorus pentachloride (PCl5). Such a method has the following reaction formula:
The α,α,α′,α′-tetrachloro-p-xylene product in the abovementioned reaction has a yield of 17–35% and is difficult to be separated.
JP79125629 (1979) discloses a method for preparing α,α,α′,α′-tetrachloro-p-xylene by reacting 4-methyl benzaldehyde with PCl5, forming an intermediate product 4-methyl,1-(dichloromethyl)benzene, and conducting a photochlorination reaction. This prior art method has the following reaction formula:
The abovementioned reaction is a two-step reaction. Even though the first step reaction has a yield of 96.5%, the second step reaction has a very low yield. The product mixture is very difficult to be purified.
George W. Kabalka; Zhongzhi Wu, Tetrahedron Lett. 2000, 41, 579–581 have published a method for preparing α,α,α′,α′-tetrachloro-p-xylene by reacting terephthaldicarboxaldehyde with BCl3. This published method has the following reaction formula:
The abovementioned reaction has a yield reaching 98%. However, BCl3 itself is a gas which makes it difficult in transportation. 1.0M BCl3 in hexane has a large volume due to its low concentration, which makes the solution difficult in transportation and is not convenient in mass production.
SOCl2 and a catalytic amount of DMF can be used in the production of chlorinated benzaldehyde or a benzaldehyde compound having a substituent on the phenyl ring thereof. For example, Melvin S. Newman, P. K. Sujeeth, J. Org. Chem., 43(22), 4367, 1978 has proposed that α,α-dichlorotoluene can be produced by reacting SOCl2/DMF with benzaldehyde.